NOTES
Nde.s
215
A department for short papers of immediate interest.
A Simplified Procedure for Synthesis of Oleic-l-C14 Acid' sUSANNE YON SCHUCHING AND ERNEST STUTZMAN
Received February 14, 1968
It, became of interest to prepare oleic-l-C14 acid in the course of metabolic studies. Bergstrom et aL2 have published a short report describing the introduction of a C14-atom in the carboxyl position by means of the nitrile synthesis. During attempts to follow their procedure, certain steps were found difficult to carry out on a small scale and were modified as described in this note. For example, the silver salt degradation method3 for the preparation of l-bromo-8,9-diacetoxyheptadecane was improved through exposure of the reactants to ultraviolet light; in addition, the temperature was kept lorn during the degradation step and the product was purified over a column of Celite mixed with silicic acid. Furthermore, a purer product was obtained when the addition of cyanide was carried out in a sealed tube. The preparation of ethyl 9,lOdibromostearate-l-CI4 and the debromination4 of this compound were modified to give a better recovery of radioactive material. It was found also that when the intermediates are prepared in pure form as described later, the ethyl 9,lO-dibromostearate-l-C14 does not require micro distillation; its purification over a column of aluminum oxide is sufficient. The synthetic steps up to the nitrile addition were carried out on a semimicro scale. The yield of radioactivity a t this point was calculated to be in excess of experimental requirements, and enough inactive dihydroxystearic acid mas added to give a total of 5 g. EXPERIMENTAL
Merck U.S.P. oleic acid was used as the starting material. Melting points were determined on a Fisher-Johns melting point apparatus and are reported as uncorrected. Double bonds were determined by the Wijs method. Bromine determinations were made by the procedure of S t e p a n ~ w . ~ (1) Supported in part by grants from the United States Public Health Service (H-1897) and The American Heart Association to C. R. Treadwell and L. Swell. ( 2 ) S. Bergstriim, K. Paabo, and M. Rottenberg, Acta Chem. Scand., 6 , 1127 (1952). (3) H. Hunsdiecker and C. Hunsdiecker, Rer., 75, 291 (1942). (4) D. E. Ames and R. E. Bowman, J. Chem. Soc., 1079 (1951). (5) A. Stepanow, Ber., 39, 4056 (1906).
The 9,10-dihydroxystearic acid ( I ) was prepared according to the method of Coleman et u Z . , ~ modified through the use of 2.5 times the recommended amount of potassium hydroxide. The yield of dihydroxystearic acid was 50%. Anal. Calcd. for CI8HJ6Oa:C, 68.3; HI 11.4. Found: C, 68.0; H, 11.3. Neutralization equivalent, calculated 324, and found, 315; m.p. 127.5'. 9,10-Diacetoxyoctadecanoic acid (11). Dihydroxystearic acid, 13.5 g., was acetylated with 15 ml. of acetic anhydride in 30 ml. of purified pyridine. The yield of 11, obtained as a light colored oil, was 16.1 g. (94%). Szlver salt of 9,10-diacetozyoctudecanoic acid (111). Of 11, 16.1 g. were taken up in 150 ml. of ethanol and neutralized to a phenolphthalein end point with sodium hydroxide. With vigorous stirring, 6 g. of silver nitrate in 90 ml. of 60% ethanol were added, light being carefully excluded. The heavy precipitate was collected, washed with water and acetone, and thoroughly dried. The white sticky product was obtained in 80% yield. l-Bromo-8,9-diacetozyheptadecane (IV). Degradation of 16.4 g. of silver salt (111) was carried out after suspending the material in 300 ml. of dry carbon tetrachloride and 16 ml. of methylene chloride. With magnetic stirring, 150 ml. of the solvent mixture were distilled off. After the residual material was cooled, 3 g. of dry silver acetate was added followed by 3.6 ml. of dry bromine dissolved in 9 ml. of carbon tetrachloride. An ultraviolet light7 was placed close to the flask and the mixture was heated gradually under reflux. Carbon dioxide started t o evolve a t 40" and the reaction was brought to completion by raising the temperature and heating a t 80' for 1 hr. Silver bromide was removed from the cooled mixture and the filtrate was washed with 2 N potassium iodide, 2 N sodium thiosulfate, and finally water and then v a s dried. This washing procedure averted troublesome emulsions. For further purification, the product was passed over a column of a mixture of 125 g. of silicic acid and 125 g. of Celite. The mixture of Celite and silicic acid had been prepared by being washed with acetone, ether, and carbon tetrachloride. Since the filtration is very slow, two chromatographic tubes, 40 X 600 mm., were employed. Adsorption was carried out in carbon tetrachloride solution and followed by elution with petroleum ether. The petroleum ether was dried down and yielded 8.9 g. (64%) of a light yellow oil. It was hydrolyzed without further purification to V. l-Bromo-8,9-dihydroxyheptadecane(V). In a solution of 300 mg. of dry hydrogen chloride in 45 ml. of dry methanol, 8.9 g. of I V was refluxed for 3 hr. Water was added and V was dissolved in ether. The solution was washed with water, dried over sodium sulfate, and gave, after evaporation, 6.9 g. of V. On recrystallization from hexane, there resulted 3.5 g. (48%) of V; m.p. 101-102". Anal. Calcd. for C17H3602Br: C, 58.4; H, 10.0; Br, 22.3. Found: C, 58.7; HI 10.1; Br, 22.3. 9,10-Dihydroxystearic-l-G~4 acid (VI) was prepared under conditions to give a pure product and a high recovery of radioactivity. Potassium cyanide (3 mmoles) containing 4 mc. of carbon14 were dissolved in 1 ml. of water and 10 ml. of ethanol in a 100 ml. Kjeldahl flask. A small excess, 1.1 g., of V was added t o the flask. The flask was sealed and heated at 100' for 48 hr. The resulting nitrile was transferred to an (6) J. E. Coleman, C. Ricciuti, and D. Sxern, J . A m . Chem. Soc., 78, 5342 (1956). (7) 6 Amp. "Mineralight," Ultra-Violet Products, Inc.
246
SOTES
alkali-resistant flasks and 2 g. of potassium hydroxide dissolved in 3 ml. of ethanol was added. Hydrolysis of the nitrile was carried out by refluxing for 48 hr. The mixture was acidified with 2N hydrochloric acid and washed with water. After being dried, VI was recrystallized from methanol. The yield was 730 mg. (82%), m.p. 127'. I n order to increase the recovery of dihydroxystearic acid, the mother liquors were reextracted with 3 g. of unlabeled dihydroxystearic acid. The total recovery of radioactivity was 3.552 mc.(88.8%). Ethyl 9,10-dibr0mostearate-l-C*~ (VII). Enough inactive dihydroxystearic acid was added t o VI to make a total of 5 g. Conversion to the dibromo-compound was carried out according to Ames and Bowman4 with the use of hydrogen hromide-acetic acid and sulfuric acid. The yield of the crude dibromide ester was 6.5 g. (88.6%). The product was esterified by refluxing in a device diagrammed in Fig. 1 with 4
b
VOL.
21
total activity was 2.4 me. (60%) based on C14-cyanide.The specific activity of the final product was 0.65 pc. per mg. RADIOISOTOPE SERVICE AND GENERAL MEDICAL RESEARCH VETERANSADMINISTRATION CENTER UT.VA. MARTINSBURG, AND
DEPARTMENT OF BIOCHEXISTRY THEGEORGEWASHINGTON UNIVERSITY OF MEDICINE SCHOOL WASHINGTON 5, D. C.
Derivatives of Piperazine. XXXI. Salts of Piperazine and N-Phenylpiperazine for Utilization in Identification of Perfluoro-Organic Acids WARNERH. CHRISTIE,JOAN B. CHRISTIE, JOHN 9.WETHINGTON, JR., A N D C. B. POLLARD Received March 31, 1958
n
In research work involving the syntheses of fluorine organic compounds, the rapid identification of perfluoro-organic acids presented a problem as suitable derivatives have not been reported. Pollard et uL1-5 have found the piperazine and Nphenylpiperazine salts of organic acids to be easily prepared and useful for identification. Haszeldine6 reported the preparation of the piperazinium salt of perfluorobutyric acid. It has been found that piperazine and N-phenylpiperazine react readily with perfluoro acids to form stable crystalline salts which can be readily purified. The monocarboxylic acids form piperazinium salts having a molecular ratio of 2 acid to 1 base. The dicarboxylic acid combines in B 1 Figure 1 to 1 molecular ratio. It is to be noted that the ml. of absolute alcohol, 10 ml. of benzene, and 0.17 ml. of piperazinium salts of the 3, 4, 6, and 8 carbon acids concentrated sulfuric acid, water being removed azeotropi- melt within about 2" of each other. Mixed melting cally. The ester VI1 was run over a short column of activated points of various combinations of these salts (apalumina which retained most of the impurities. A sample proximately 50-50) show depressions of about 6". had a b.p. of 235" a t 1 mm.; bromine content calculated for C20H3802BrI:Br, 34%. Found: 34.5%. The ester was a pale The N-phenylpiperazinium salts of the 3 carbon yellow oil. The yield was 5.1 g. (85%). It was used for the acid and Kel F 8114 melt within 3" of each other. preparation of oleie-l-Cl* acid without further purification. A mixture of these two salts (approximately 50Oleic-l-Cl4 acid (VIII). Of zinc, 3 g. were activated by 50) shows a depression of about 30". The N being boiled 5 min. with 15 ml. of ethanol and 1 ml. of 60% phenylpiperazinium salts of the 4, 6, and 8 carbon aqueous hydrobromic acid. The ethyl ester of VI1 was added to the zinc and the mixture refluxed under nitrogen for 2 acids melt close together. Mixtures of various comhr. The zinc was removed by filtration and extracted with binations of these salts (approximately 50-50) 1 g. of carrier ethyl oleate in petroleum ether for a more show depressions of from 15 to 20". The mixed complete recovery of radioactive material. The combined melting points were determined in sealed tubes. filtrates were washed with 5% sulfuric acid and water and the solution was dried. Product VI11 can be saponified directly without distillation. Saponification of the ethyl oleate was carried out with sodium ethoxide in absolute alcohol, followed by acidification with 2hr hydrochloric acid. The yield of oleic-l-C1* acid was 3.7 g., m.p. 12'; iodine number calculated, 89.9. Found: 91.6. Radioactivity was determined by counting an infinitely thick sample after diluting with cold oleic acid in a gas-flow chamber.8 The (8) Corning "Boron Free." (9) RCL Nucleometer, Scaler Type, Mark 9, Model 4.
(1) C. B. Pollard and D. E. Adelson. 6.Am. Chem. Soc., 56,' 150 (1934). ( 2 ) C. B. Pollard, D. E. Adelson, and J. P. Bain, J . A m . Chem. SOC.,56, 1759 (1934). (3) C. B. Pollard j n d 11. E. Adelson, J . Am. Chem. SOC., 58,532 (1936). (4) R1. Prigot and C. R. Pollard, J. A m . Chern. SOC.,70, 2758 (1948). ( 5 ) C. B. Pollard and K. 8. Gidwani, J . Ora. Chem., 22, 992 (1957). (6) R. N. Haszeidine, J. Chem. Soc., 2789 (1950).
